I've decided to take your advise, and finally purchase a battery monitor. Am I correct to understand that it is common to use a monitor for the house battery only? And that a simple voltage meter is sufficient for a pure starting battery? What happens when my battery switch is set to 1+2 combined? Will the monitor readings still be accurate? Thanks, You're awesome! - Captain Hippy
Battery monitors are mostly used on deep cycle batteries. For start batteries, a voltmeter is usually quite adequate for monitoring battery health. A battery monitor installed on house batteries will always monitor any amps going in and out of the battery bank. With the battery switch to set to both, the portion of amps taken from the house battery will be shown on battery monitor. The engine battery will also be assisting with running loads or charging and those amps will not show on the house battery monitor.